The major goal of this proposal is to obtain new information concerning the process of vertebrate skeletal mineralization at the molecular and cellular level. An understanding of mineralization is significant because it is the foundation for mechanical support of the body, for skeletal adaptation under mechanical constraint, as an ion reservoir, and for treating, preventing, and curing a variety of skeletal abnormalities that affect human well being. The proposed study will focus on three model systems, the calcifying tendon from normal turkeys, long bone from exercised mice, and a tissue-engineered model of phalanges and small joints. These systems will be examined under natural conditions and after changes that alter mechanical forces acting on them. A combination of molecular biological, biochemical, immunochemical, and structural techniques will be used to determine the processes by which cells elaborate an organic matrix that mineralizes, as well as the chemical and structural nature of matrix-mineral interaction. The specific hypothesis to be examined is: the structural and functional adaptation of a calcifying tissue to mechanical perturbation is directed by expression of osteopontin (opn), osteocalcin (oc) and bone sialoprotein (bsp), and their interactions with mineral deposition. The Specific Aims that will probe this structure-function relationship are to (1) establish the expression pattern of the selected genes (opn, oc, bsp) as compared to specific matrix proteins, matrix receptors, cytoskeletal proteins and mineral formation in the three model systems; (2) determine the adaptive response at the tissue level in terms of these parameters following perturbation of the tendon model altered by a surgically-induced mechanical change, and of the bone model through exercise; and (3) assess the adaptive response at the organ level by determining the pattern of protein expression and protein-mineral interactions in the phalanx-joint model placed under a muscular load. This multifaceted approach will contribute to an increased understanding of the chemistry, structure, organization, and interactions of relevant molecules and cells that are critically important for the function of mineralizing tissues and their adaptation under mechanical loading.